Prosthetic article and method for manufacture

ABSTRACT

There is disclosed a prosthetic article formed of an alloy containing 12-20 percent chromium; 7-12 percent cobalt; 1.5-5 percent of at least one of molybdenum, tungsten, columbium, and tantalum; 5-9 percent of at least one aluminum and titanium; 0.05-0.2 percent carbon; 0.005-0.1 percent boron; 0.05-0.2 percent of at least one of zirconium and hafnium; and the balance nickel, which may receive a strongly bonded, fused, inorganic oxide coating; and a method for manufacturing the article which includes melting the alloy in air, forming the prosthetic device, coating at least part of its surface with a coating capable of forming a fused inorganic oxide and then firing the coated article to fuse the inorganic oxide.

ifizaited States Patent 1 1 Kulwiec PROSTHETIC ARTICLE AND METHOD FORMANUFACTURE [75] Inventor: Leonard Kulwiec, Santa Rosa, Calif.

[73] Assignee: Sterndent Corporation, Mt. Vernon,

22 Filed: May 2,1974

21 Appl.N0.: 466,167

52 Us. (:1 32/10 A; 32/10 A [51] Int. Cl. A6lc 13/00 [58] Field ofSearch 3/l.9, 1.91, 1.912, 1.913;

128/92 C, 92 CA; 32/8, 15, 2, 10 A [56] References Cited UNITED STATESPATENTS 3,466,748 9/1969 Christensen 32/10 A 3,606,615 9/1971 Rudiger32/10 A 3,787,900 1/1974 McGee 32/10 A 14 1 July 29, 1975 PrimaryExaminer-Robert Peshock Attorney, Agent, or Firm-Warren, Rubin &Chickering [57] ABSTRACT There is disclosed a prosthetic article formedof an alloy containing 12-20 percent chromium; 7-12 percent cobalt;1.5-5 percent of at least one of molybdenum, tungsten, columbium, andtantalum; 5-9 percent of at least one aluminum and titanium; 0.050.2percent carbon; 0.0050.l percent boron; 0.05-0.2 percent of at least oneof zirconium and hafnium; and the balance nickel, which may receive astrongly bonded, fused, inorganic oxide coating; and a method formanufacturing the article which includes melting the alloy in air,forming the prosthetic device, coating at least part of its surface witha coating capable of forming a fused inorganic oxide and then firing thecoated article to fuse the inorganic oxide.

13 Claims, No Drawings PROSTHETIC ARTICLE AND METHOD FOR MANUFACTUREBAKCGROUND OF INVENTION Prosthetic devices, particularly those used indental work, must be strong, corrosion resistant, esthetically pleasingand compatible with living tissue. lnaddition, the prosthetic devicesmust be of material which can be readily formed into complicated shapes.

Metals used for dental prosthetic devices must also be capable ofaccepting inorganic oxide coatings such as dental procelain. To do this,the metals must have a compatible oxide coating on their surface. Acompatible oxide coating is one that forms a bond with the fusedinorganic oxide coating which is. applied later. Alloys used in dentalprosthetic devices must also have a coefficient of thermal expansion nottoo different from that of the fused inorganic oxide coatings that areused in conjunction with them, otherwise the temperature cyclingexperienced in applying and fusing one or more layers of inorganic oxidecoating would result in cracking of the coating and sloughing off ifgreat differences in thermal expansion were experienced between theoxide and the metal.

Metals used for prosthetic devices in the past were precious metals,particularly gold. The high cost of gold due to its natural scarcity andcompeting uses in making jewelry unnecessarily exaggerate the cost ofprosthetic devices. In addition, the low tensile strength of gold makesgold not entirely satisfactory in some respects. Although gold readilyaccepts a porcelain coating, it frequently requires a separate bondinglayer because its natural oxide layer is not adequate in all respectsfor bonding porcelain. Of course, for large prosthetic devices, such asthose used for restoring hip joints, the use of gold would beprohibitively expensive.

Non-precious dental alloys have been known in the past. One such alloyis an alloy that is primarily nickel and includes beryllium as acritical alloying element. This alloy is described in US. Pat. No.3,749,570. Although the alloy has satisfactory physical properties,problems are encountered both in the preparation of the alloy and in thepreparation of devices from it because of the highly toxic nature ofberyllium. All processes in forming such an alloy into a suitableprosthetic device must be carried on with extreme caution so that fumes,dust, or other forms of the alloy or its compounds are not inhaled oringested by workers. Particularly in small laboratories, such as thosein individual dentists offices, it is very difficult if not impossibleto provide adequate safety measures for using such a dangerous material.Even if adequate safety equipment is available, it is difficult toinsure that all workers in the laboratories are sophisticated enough tounderstand the hazards of working beryllium alloys and to employ thesafety devices that are available.

SUMMARY OF INVENTION This invention avoids or greatly mitigates all ofthe problems enumerated above. The invention includes a prostheticdevice made of a non-precious alloy which forms a natural oxide coatingthat is not only compatible with conventional fused inorganic oxidesapplied to dental devices, but actually participates in the bond betweenthe fused inorganic oxide and the metal. The expansion and contractionof the alloy with changes of temperature correspond so closely with theexpansion and contraction of the fused inorganic oxides that cracking ofthe fused oxides is avoided. The alloy also does not contain highlytoxic materials so that it may be melted, cast, ground, and otherwiseworked without special precautions to avoid toxic effects.

As used in this specification, the term prosthetic device is defined asa metal device that is attached to a living animal in direct contactwith living tissue to replace a missing part or to repair amalfunctioning part. Prosthetic devices may be as simple as metal.inlays to fill teeth but are usually more complex, such as caps forteeth, bridges, plates or implants in bones of legs, jaws, etc. The termfused inorganic oxide refers to a substance made of inorganic oxidehaving its physical form altered by being subjected to high temperature.Typically a fused inorganic oxide is glazed porcelain or a vitreousmaterial such as those used in detnal work. The term bony tissue refersto any hard bone-like tissue and includes tissue such as teeth. The termbonded is defined to mean: firmly fixed to a surface without the use ofan intermediary bonding material such as organic cement.

The alloys employed in the articles of this invention are thosecontaining from 12-20 percent chromium; from 7-12 percent cobalt; from1.5-5 percent of at least one of molybdenum, tungsten, columbium, ortantalum; from 5-9 percent of at least one of aluminum and titanium;from 0.5-0.2 percent carbon;- from 0.005-0.1 percent boron; from 0.050.2percent of at least one of zirconium and hafnium; and the balancesubstantially nickel. The alloy is formed usually by melting in air andthen casting, after which it may or may not be coated completely orpartially with a fused inorganic oxide coating that is bonded to itssurface. The article is shaped to conform to, and to be attached to,bony tissue of a living animal. The alloy has been found to be entirelycompatible not only with the bony tissue to which it is attached butalso with soft tissue with which it is in contact. For example, a capfora tooth made from the alloy of this invention coated with porcelaincan be worn comfortably indefinitely by a human being. Neither theporcelain nor the alloy reacts unfavorably with the tooth or the gums,and the, alloy is corrosion resistant enough to remain uncorroded incontact with body fluids and to resist galvaniceffects with differentmetals such as may be found withinthe mouth. By way of example, a personhaving a cap made of the alloy referred to above in his mouth along witha gold filling in a different tooth and a silver amalgam filling instill a different tooth will have no galvanic reaction set up betweenthe cap and the other metals to destroy any of the metals or to creatediscomfort.

The alloy of this invention must contain the essential ingredientsenumerated above; however, other ingredients may also be included withinits composition. One particularly useful alloy that is commerciallyavailable contains 15-18 percent chromium, 8-11 percent cobalt, 0.75-2.2percent molybdenum, 1.8-3 percent tungsten, 0.5-2 percent columbium, l-3percent tantalum, 3-4 percent aluminum, 0.1-2 percent carbon, 3-4percent titanium, 0.01-0.05 percent boron, 0.0l-0..2 percent zirconium,and the balance nickel. This alloy is described in US. Pat. No.3,459,545 as an alloy suitable for turbine blades in gas turbineengines.

The alloys described above are suitable to be shaped by any of thetechniques usually employed in forming prosthetic devices for alloys.Particularly for dental prosthetic devices, the initial step in shapingan alloy involves melting it in air and casting it. The resulting castarticle has a thin oxide coating which adheres tightly to the metal andis compatible with the fused inorganic oxides that are generallyemployed for coating such prosthetic devices. The fused inorganic oxidesare primarily silicon oxide and aluminum oxide or various compounds ofsilicon, aluminum and oxygen. Photomicrographs of the bond between thealloys described above and such materials as dental porcelain indicatethat the bond is not effected at a sharp interface between the porcelainand the metal oxide layer. Rather, the natural oxide coating on themetal merges with the fused inorganic oxide to create a deep bond thathas a composition gradient from the surface of the metal to the fusedinorganic oxide coating. It is speculated that this deep bond,indicating a special compatibility between the fused inorganic oxidesand the metal oxide coating, is the reason for the extremely firm bondthat permits the alloy of this invention to be coated with fusedinorganic oxides that do not crack during temperature cycling or chipoff when subjected to compressive forces or abrasion.

The fused inorganic oxides may be glazed, as dental porcelainis, or theymay be porous, for example in the form of a porcelain bisque Fuseddental porcelain may be applied in several layers, as is conventional inthe art. For example, the metal shaped as a prosthetic device may firstbe coated with an opaque layer to mask the metal, after which it iscoated with a porcelain layer, and finally coated with a vitreous enamellayer to produce a natural, translucent, tooth-like appearance.

If the metal prosthetic device is to be implanted directly in bonytissue, it preferably is coated with porcelain bisque. Porcelain bisqueis compatible with living tissue and is porous enough for fibrous tissueto grow into the pores thereby forming a firm connection between thebony tissue and the prosthetic device. For example, an artificial hipjoint may be made so that the portion connected to the femur is coatedwith porcelain bisque. An alloy pin so made will not only be compatiblewith bone tissue but will permit fibrous bone tissue to grow in thepores of the porcelain bisque to effect a very firm connection. Thoseportions of dental prosthetic devices that are implanted directly injawbones also are preferably coated with porcelain bisque.

DETAILED DESCRIPTION OF INVENTION To better describe the process of thepresent invention as employed to make devices of the present invention,following is a specific example of the process employed to make such anarticle. The process described is one for making a cap for a damagedtooth. The cap is formed of the alloy of this invention and a portion ofthe exterior of the cap is coated with dental porcelain.

A wax model of the cap is prepared by conventional techniques. The waxmodel is surrounded with what is referred to in this art as high-heatoxy-phosphate investment, and a wax insert is appropriately placed toform a sprue. Wax is removed from the investment by heating theinvestment to 700F for thirty minutes followed by a burnout for 1 hourat 1600F. Afterwards, the investment is fixed in a conventionalcentrifical casting device; and an alloy containing 16 percent chromium,percent cobalt, 2 percent molybdenum, 2.5 percent tungsten, 1 percentcolumbium, 1.25 percent tantalum, 3.5 percent aluminum, 3.5 percenttitanium, 0.18 percent carbon, 0.02 percent boron, 0.1 percentzirconium, and 59.95 percent nickel is placed in a quartz crucible andmelted wit a torch fed with acetylene and oxygen. A gas mixture obtainedby setting oxygen pressure at 10 psi and acetylene pressure at 8 psi isemployed. The alloy melts at a temperature slightly higher than 2450F asindicated by the metal in the crucible slumping. A casting flux is addedwhen the alloy begins to slump; and when the temperature is raisedslightly higher the alloy becomes very fluid and forms in the shape of asphere in the crucible. When the alloy is highly fluid it is allowed torun from the crucible into the mold.

After solidification and cooling, the casting is removed from the mold,and it is worked on as necessary with burrs or other tools, after whichit is thoroughly cleaned by sandblasting with fine sand. Copings can bedressed down to 0.1-0.2 mm, which is about half the thickness requiredfor gold dental alloys.

Areas to be covered with porcelain are fine-ground, and other areas maybe polished ifdesired. The castings are thoroughly scrubbed withammonium hydroxide and dried. No degassing or acid treatment isnecessary to further prepare the surfaces to receive porcelain.Conventionally used and commercially available porcelains and vitreousmaterials are applied and used in accordance with the manufacturersdirections. All of the commercially available porcelains for dental useare entirely compatible with the casting and, in fact, form strongerbonds than when used with the dental alloys of the prior art. After theporcelain work is completed, the porcelain is covered with a soft wax;the cap is sandblasted and polished. Using ordinary polishingtechniques, the alloy will take a brilliant luster, known in the art asa high micron luster, which resists corrosion and the formation ofdental plaque. The cap may then be fixed in the mouth of the patient bythe known dental techniques.

What is claimed is:

1. An article comprising a solid alloy comprising from about 12-20percent chromium, from about 7-12 percent cobalt, from about 1.5-5percent of at least one element selected from molybdenum, tungsten,columbium and tantalum, from about 5-9 percent of at least one elementselected from aluminum and titanium, from about 0.05-0.2 percent carbon,from about 0.005-0.1 percent boron, from about 0.050.2 percent of atleast one element selected from zirconium and hafnium and the balancenickel which is shaped to conform with the shape of bony tissue of aliving animal and for attachment to said bony tissue.

2. The article of claim 1 wherein said bony tissue is a tooth.

3. An article comprising a solid alloy comprising from about 12-20percent chromium, from about 7-12 percent cobalt, from about 1.5-5percent of at least one element selected from molybdenum, tungsten,columbium and tantalum, from about 5-9 percent of at least one elementselected from aluminum and titanium, from about 0.050.2 percent carbon,from about 0.005-0.l percent boron, from about 0.05-0.2 percent of atleast one element selected from zirconium and hafnium and the balancenickel, having a fused inorganic oxide bonded to the surface thereof.

4. The article of claim 3 wherein said alloy consists essentially of15-18 percent chromium, 8-11 percent cobalt, 0.75-2.2 percentmolybdenum, 1.8-3 percent tungsten, 0.5-2 percent columbium, 1-3 percenttantalum, 3-4 percent aluminum, 0.1-0.2 percent carbon, 3-4 percenttitanium with a total content of aluminum and titanium not exceeding 7.5percent, 0.01-0.05 percent boron, 0.0l-0.2 percent zirconium and thebalance essentially nickel.

5. The article of claim 3 wherein said fused inorganic oxide is dentalporcelain.

6. The article of claim 3 wherein said fused inorganic oxide is ceramicbisque.

7. The article of claim 3 shaped to conform with the shape of bonytissue of a living animal for attachment to said bony tissue.

8. The article of claim 7 wherein said bony tissue is a tooth.

9. A process for producing a prosthetic device comprising:

A. Forming a shaped article of an alloy comprising from about 12-20percent chromium, from about 7-12 percent cobalt, from about 1.5-5percent of at least one element selected from molybdenum, tungsten,columbium and tantalum, from about 5-9 percent of at least one elementselected from aluminum and titanium, from about 0.05-0.2 percent carbon,from about 0.0050.1 percent boron, from about 0.05-0.2 percent of atleast one element selected from zirconium and hafnium and the balancenickel, said article being shaped for attachment to bony tissue of aliving animal;

B. Covering at least a portion of the surface of said shaped articlewith inorganic oxide capable of forming a fused inorganic oxide coatingat elevated temperature; and

C. Heating said shaped article covered with inorganic oxide to atemperature at which a fused inorganic oxide coating is formed.

10. The process of claim 9 wherein said alloy consists essentially of15-18 percent chromium, 8-11 percent cobalt, 0.75-2.2 percentmolybdenum, 1.8-3 percent tungsten, 0.5-2 percent columbium, 1-3 percenttantalum, 3-4 percent aluminum, 0.1-0.2 percent carbon, 3-4 percenttitanium with a total content of aluminum and titanium not exceeding 7.5percent, 0.01-0.05 percent boron, 0.01-0.2 percent zirconium and thebalance essentially nickel.

11. The process of claim 9 wherein said shaped article is formed bycasting.

12. The process of claim 9 wherein said prosthetic device is for use inan oral cavity.

13. A physiologically compatible prosthetic alloy consisting essentiallyof from about 12-20 percent chromium, from about 7-12 percent cobalt,from about 1.5-5 percent of at least one element selected frommolybdenum, tungsten, columbium and tantalum, from about 5-9 percent ofat least one element selected from aluminum and titanium, from about0.05-0.2 percent carbon, from about 0.0050.1 percent boron, fromab0ut-0.050.2 percent of at least one element selected from zirconiumand hafnium and the balance nickel.

UNITED STATES PATENT AND TRADEMARK OFFICE EERTIFICATE OF CORRECTIONPATENT NO. 3,896,547

|N\/ ENTOR(S) Leonard Kulwiec It is certified that error appears in theabove-identified patent and that said Letters Patent Q are herebycorrected as shown below:

Column 2, line 17, change "detnal" to read -dental-;

line 28, change "0.5-0.2" to read -0.o5-0.2--; line 67, before "alloyscorrect "for" to read --from--; and

Column 4, line 4, after "melted" correct "wit" to read -with--..

Column 5, line 26, change "0.0050.l" to read -0. 0O50. l--= a Signed andScaled thus second Day of December 1975 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL BARN Arresting Officer Commissioner ofParenlsand Trademarks

1. AN ARTICLE COMPRISING A SOLID ALLOY COMPRISING FROM ABOUT 12-20 PERCENT CHROMIUM, FROM ABOUT 7-12 PERCENT COBALT, FROM ABOUT 1.5-5 PERCENT OF AT LEAST ONE ELEMENT SELECTED FROM MOLYBDENUM, TUNGSTEN, COLUMBIUM AND TANTALUM, FROM ABOUT 5-9 PERCENT OF AT LEAST ONE ELEMENT SELECTED FROM ALUMINUM AND TITANIUM, FROM ABOUT 0.05-0-2 PERCENT CARBON, FROM ABOUT 0.005-0.1 PERCENT BORON. FROM ABOUT 0.05-0.2 PERCET OF AT LEAST ONE ELEMENT SELECTED FORM ZIRCONIUM AND HAFNIUM AND THE BALANCE NICKEL WHICH IS SHAPED TO CONFORM WITH THE SHAPE OF BONY TISSUE OF A LIVING ANIMAL AND FOR ATTACHMENT TO SAID BONY TISSUE.
 2. The article of claim 1 wherein said bony tissue is a tooth.
 3. An article comprising a solid alloy comprising from about 12-20 percent chromium, from about 7-12 percent cobalt, from about 1.5-5 percent of at least one element selected from molybdenum, tungsten, columbium and tantalum, from about 5-9 percent of at least one element selected from aluminum and titanium, from about 0.05-0.2 percent carbon, from about 0.005-0.1 percent boron, from about 0.05-0.2 percent of at least one element selected from zirconium and hafnium and the balance nickel, having a fused inorganic oxide bonded to the surface thereof.
 4. The article of claim 3 wherein said alloy consists essentially of 15-18 percent chromium, 8-11 percent cobalt, 0.75-2.2 percent molybdenum, 1.8-3 percent tungsten, 0.5-2 percent columbium, 1-3 percent tantalum, 3-4 percent aluminum, 0.1-0.2 percent carbon, 3-4 percent titanium with a total content of aluminum and titanium not exceeding 7.5 percent, 0.01-0.05 percent boron, 0.01-0.2 percent zirconium and the balance essentially nickel.
 5. The article of claim 3 wherein said fused inorganic oxide is dental porcelain.
 6. The article of claim 3 wherein said fused inorganic oxide is ceramic bisque.
 7. The article of claim 3 shaped to conform with the shape of bony tissue of a living animal for attachment to said bony tissue.
 8. The article of claim 7 wherein said bony tissue is a tooth.
 9. A process for producing a prosthetic device comprising: A. Forming a shaped article of an alloy comprising from about 12-20 percent chromium, from about 7-12 percent cobalt, from about 1.5-5 percent of at least one element selected from molybdenum, tungsten, columbium and tantalum, from about 5-9 percent of at least one element selected from aluminum and titanium, from about 0.05-0.2 percent carbon, from about 0.0050.1 percent boron, from about 0.05-0.2 percent of at least one element selected from zirconium and hafnium and the balance nickel, said article being shaped for attachment to bony tissue of a living animal; B. Covering at least a portion of the surface of said shaped article with inorganic oxide capable of forming a fused inorganic oxide coating at elevated temperature; and C. Heating said shaped article covered with inorganic oxide to a temperature at which a fused inorganic oxide coating is formed.
 10. The process of claim 9 wherein said alloy consists essentially of 15-18 percent chromium, 8-11 percent cobalt, 0.75-2.2 percent molybdenum, 1.8-3 percent tungsten, 0.5-2 percent columbium, 1-3 percent tantalum, 3-4 percent aluminum, 0.1-0.2 percent carbon, 3-4 percent titanium with a total content of aluminum and titanium not exceeding 7.5 percent, 0.01-0.05 percent boron, 0.01-0.2 percent zirconium and the balance essentially nickel.
 11. The process of claim 9 wherein said shaped article is formed by casting.
 12. The process of claim 9 wherein said prosthetic device is for use in an oral cavity.
 13. A physiologically compatible prosthetic alloy consisting essentially of from about 12-20 percent chromium, from about 7-12 percent cobalt, from about 1.5-5 percent of at least one element selected from molybdenum, tungsten, columbium and tantalum, from about 5-9 percent of at least one element selected from aluminum and titanium, from about 0.05-0.2 percent carbon, from about 0.005-0.1 percent boron, from about 0.05-0.2 percent of at least one element selected from zirconium and hafnium and the balance nickel. 